A typical vehicle air bag module comprises a folded air bag and an inflator which are disposed in a container. When the vehicle is involved in a collision, a crash signal initiates operation of the inflator. The inflator generates an inert gas (e.g., nitrogen) which forces the air bag out of the container and inflates the air bag. An air bag module is located in a vehicle so that the air bag, when forced out of the container, will cushion a vehicle occupant against impact with a structural part of the vehicle. One location for an air bag module is in the instrument panel or dashboard on the passenger side of the vehicle.
A known type of container for a passenger side air bag module comprises a receptacle with walls forming a closed end, an open end, and an internal cavity disposed between the closed and open ends. A cover covers the open end and closes the receptacle. The inflator and the folded air bag are located in the internal cavity and are coupled to respective portions of the receptacle. The cover is adapted to separate when pressure is applied to it. During an emergency, therefore, the air bag can be forced through the cover as the air bag is being inflated.
To assemble the module, the air bag and inflator are loaded into and coupled to the receptacle. The inflator is disposed adjacent the closed end of the receptacle, and the folded air bag located adjacent the open end of the receptacle. Thereafter, the cover is attached to the receptacle to complete the module.
After the module is assembled, it is installed as a unit into a vehicle. With a passenger side air bag module, the receptacle is located just behind the vehicle dashboard, and is fastened to a structural part of the vehicle. The cover has an outer surface profile that matches the outer profile of the dashboard. Due to the location of the receptacle, the cover is effectively incorporated into and forms a part of the vehicle dashboard.
During inflation of an air bag, the receptacle, which is generally made of metal (e.g., steel sheet), must withstand significant pressures. Specifically, a passenger side inflator, when actuated, is believed to produce gas pressure of approximately 30-50 psi in the container. It has been found that under such pressure, portions of the open end of the receptacle may tend to bulge outward or "fishmouth" during deployment of the air bag. When the container is located just behind the vehicle dashboard, fish-mouthing of the open end of the receptacle can crack (or deform) the dashboard. Such cracking or deformation will require replacement of the entire dashboard.
One known technique for resisting fish-mouthing of a metal air bag receptacle is to bend outward certain portions of the metal walls forming the open end of the receptacle outward. The walls are bent in the areas which are most prone to fish-mouthing. This technique increases the beam strength of those portions of the walls to resist fish-mouthing. Another technique for resisting fish-mouthing of an air bag receptacle is disclosed in U.S. Pat. No. 4,842,300 to Ziomek et al. In the Ziomek, et al. patent, a reaction member, preferably an inelastic fabric tether strap, extends across the open end of the receptacle. At its ends, the tether strap is connected to the portions of the walls of the receptacle most prone to fish-mouthing. The tether strap restrains those portions of the walls of the receptacle from bulging outward under the pressures of air bag deployment.
Applicants also believe that it is desirable physically to separate the air bag from the inflator within an air bag module. Such separation ensures that during assembly of the module and during normal operation of a vehicle, the inflator and the air bag do not interfere with each other. Moreover, during inflation of the air bag, the inflator becomes quite hot. Separation of the air bag from the inflator helps prevent the air bag from contacting and being burned by the inflator.
Still further, applicants believe that the receptacle, the air bag, and the other components which make up the module be designed for efficient and effective fabrication and assembly into the module, preferably by mass production techniques.